Energy scarcity brought on by the overuse of fossil fuels and severe environmental contamination pose substantial dangers to society. Solutions to the pressing environmental and energy issues facing the globe can be addressed by using semiconductors as photocatalysts for endergonic water splitting. By combining electron-rich TiO₂ (n-type) and hole-rich NiO (p-type) semiconductors, p-n heteronanojunctions can be created for spatial exciton separation, mitigating the undesirable fates of excitons. We designed and employed a synthetic route in which nickel domains could epitaxially nucleate and grow through the reduction of Ni precursors by oleylamine on the surface of prefabricated anatase TiO₂ nanorods. The morphology, structural, and optoelectronic properties of nanocrystals were characterized using transmission electron microscopy (TEM), high-resolution TEM, STEM-EDS, STEM HAADF, powder X-ray diffraction, UV-visible spectroscopy, and fluorescence spectroscopy. We observe TiO₂ nanorods multiply decorated with {200} faceted cubic NiO nanocrystals with a diameter of 4.1 ± 0.8 nm. The NiO-TiO₂ hybrid nanocrystals were supported on amorphous fumed silica. Irradiation of the photocatalyst with UV light in aqueous solution generated trace quantities of hydrogen gas even in the presence of methanol as a hole scavenger. While employing AgNO₃ as electron scavenger we observe fast formation of metallic silver and formation of H₂O₂. The rate of formation of H₂O₂ was rapid initially but concurrent decomposition of H₂O₂ resulted steady state concentration. The following processes were dominant in photocatalysis experiments with SiO₂/NiO-TiO₂: the one-electron oxidation of hydroxide ions to hydroxyl radicals, the equilibrium established between hydroxyl radicals and hydrogen peroxide, and the subsequent one-electron reduction of hydroxyl radicals back to hydroxide ions, completing a closed chemical cycle. Introducing a faster one-electron reduction pathway leads to increased steady-state concentration of H₂O₂.

James Hoefelmeyer

Appearances